1. Field of the Invention
The present invention relates to an electronically controlled suspension system, and more particularly, to an electronically controlled suspension system capable of securing ride comfort and control stability.
2. Description of the Related Art
Generally, a suspension system is a shock-absorbing apparatus comprising a shock absorber or spring installed between an axle and a frame of a vehicle, and serves to make the vertical movement of the vehicle smooth and to absorb a shock or vibration transmitted from a road surface so that the shock or vibration cannot be transmitted to a vehicle body of the vehicle.
Hereinafter, a conventional electronically controlled suspension system will be described with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a conventional electronically controlled suspension system.
As illustrated in FIG. 1, the electronically controlled suspension system comprises a sensor unit 10 for detecting and providing vertical acceleration components using vertical acceleration sensors mounted at portions of a vehicle body on the sides of front and rear road wheels of a vehicle; a signal processing unit 20 for detecting a velocity component from a signal outputted from the sensor unit 10; a control command value calculating unit 30 for calculating a control command value using a signal outputted from the signal processing unit 20 and a predetermined control gain K; and damper driving units 40 such as actuators for controlling damping forces of variable dampers 50 based on the control command value.
At this time, the damper driving unit 40 such as an actuator, e.g., a solenoid valve or a step motor, is connected to the variable damper 50. The variable damper 50 has two or more damping force characteristic curves such as hard and soft modes. At this time, the variable damper 50 changes a damping force continuously or at multiple stages in response to the driving of the damper driving unit 40. Here, the damper driving unit 40 drives the variable damper 50 based on the control command value from the control command value calculating unit 30. Accordingly, the variable damper 50 generates a damping force to suppress transmission of vibration from a road surface to the vehicle body, thereby improving ride comfort or preventing a variation in a ground contact force to enhance control stability of the vehicle.
The control command value to be outputted to the damper driving unit 40 for controlling the variable damper 50 is calculated by the control command value calculating unit 30. The control command value calculating unit 30 uses a predetermined constant value as the control gain K that is utilized in calculating such a control command value. If the control gain K used for the calculation of the control gain has been set to a large constant value and a high frequency signal representing an uneven road surface is inputted from the signal processing unit 20 to the control command value calculating unit 30, the control command value calculating unit 30 outputs a relatively large control command value in response to the large control gain K, and the damper driving unit 40 controls the variable damper 50 in hard mode according to the large control command value with respect to the uneven road surface for which soft mode control is required. Thus, there is a problem in that ride comfort is deteriorated.
On the other hand, if the control gain K has been set to a small constant value and a low frequency signal representing a wavy road surface is inputted from the signal processing unit 20 to the control command value calculating unit 30, the control command value calculating unit 30 outputs a relatively small control command value in response to the small control gain, and the damper driving unit 40 controls the variable damper 50 in soft mode according to the small control command value with respect to the wavy road surface for which hard mode control is required. Thus, there is a problem in that ride comfort is deteriorated.